1. Field of Invention
The present invention relates generally to the field of fluid transfer, and more specifically to submersible and surface pump apparatus and systems and methods of making and using same.
2. Related Art
Vertical and horizontal centrifugal pump systems are designed to operate in downthrust mode, where pressure inside the pump case by action of the pump impellers tends to exert an axial force on the pump shaft toward the suction inlet. Most pump and motor manufacturers instruct users not to operate these pumps in upthrust mode, where pressure exerted by pumped fluid against the impellers at the suction inlet may result in damaged impellers, a damaged pump shaft, and damaged pumps seals and bearings. Upthrust conditions may exist at startup, when operating at high flow rates, and/or when the specific gravity of the fluid being pumped changes. In the upthrust condition, bearings may not be cooled sufficiently due to lack of recirculation and may fail. Some pump manufacturers use a disk-type upthrust pad at the discharge/exit area of the pump to limit the upthrust movement of the shaft. Other pump manufactures have used combinations of a grooved upthrust pad in the diffuser and grooved radial bore in the diffuser to prevent the loss of lubrication to the bearing in the upthrust condition. These approaches are not always successful.
It is evident that there is a need in the art for pump apparatus and methods which more adequately address the upthrust condition problem.